Onyehn 1 Channel DC 3V Relay High Level Driver Module Optocoupler Relay Module Isolated Drive Control Board for Arduino (Pack of 8)

Worked good. Open board in the back makes me nervous though

These use a Sharp PC817X photocoupler which is quite compatible with Raspberry Pi 3V3 GPIO signals. The jumpers allow you to optionally isolate the photocoupler so nothing but the passive diode is connected to the Pi, and a separate supply powers the relay coils. The diode only requires a few mA to switch, so it's not a current burden on the RPi GPIO individual pin limits or the overall budget.The build quality is such that these are more of a kit for you to finish than a ready-to-run module. All 5 of 5 units worked out of the box, but inspection showed the solder work was poor with lots of gaps and globs. The modules were all covered in what appeared to be a dirty evaporated flux cleaning solvent, with gummy bits of residue everywhere. One module appeared to be a manual rework, with flux all over several components' solder joint areas, that hadn't been cleaned at all.

I've had this in operation for several months without issue. I use it to control the opening and closing my chicken coop door remotely through a raspberry PI. IT stays active for as long as there is a signal going to the "in" terminal from a gpio pin on the pi. VCC In and GND are the pi side (whats giving the commands). NC, COMM, and NO are for the circuit being controlled. "NC is normally closed" "NO is Normally Open" and Comm is where the power source is switched. to only have power while "IN" is triggered connect the target device to "NO" to interrupt power to the target device when the "IN" is triggered connect the target to "NC".Update 5:/6/2020 after a year the relays that I have in use are still working well, these have BSTEP mechanical relays powered by the 3.3v line on my pi's. Two modules have "Songle" branded mechanical relays. These require more power to actuate, and required implementing an external power source for their coils. Other than the brand, the markings and ratings are the same.The Jumpers on the board connect the VCC and Ground screw terminals the relay. If you remove the jumpers you can connect a separate power supply to the pins closest to the relay, thus optically isolating the trigger source from the power. (this makes the VCC screw terminal useless, you still use the trigger + ground screw terminal for the trigger).

These work well for the intended purpose. I had to find a controller that stated specifically that they worked with 3v micro-controllers (like those made by Adafruit). Happy to report these work perfect for me needs (automated greenhouse).

I used these with a nodemcu (esp8266) running ESPHome to create a home brewed smart irrigation system controlled via Home Assistant.